It said: "Dennis Bates worked for 12 years for the Inland Revenue, specialising in the tax affairs of small businesses and is eminently qualified to provide advice."

"The Green Book which sets out the rules and advice on behalf of the Parliamentary authorities states specifically that professional advice, for example on tax and legal matters, is an allowable expense.

"Many MPs rightly seek professional assistance and advice where this relates specifically to their role as members of Parliament and the expense is therefore legitimate and justifiable. The purpose of this is to ensure all tax liabilities connected with parliamentary duties are properly dealt with."

Treated differently

Schools minister Mr Knight told the BBC he had used a different accountant until 2005 who had charged £763.75 for advice - compared with the £345 Mr Bates charged.

"Anyone listening who does as a - you know, for their small business or whatever - use an accountant, will know that you can't buy much for £345," he said.

"What it is, is just making sure that I'm paying the proper amount of tax so that I'm not falling foul of what one or two of my colleagues have done, where they've tried to avoid paying the full amount of tax that they should do."

But the Federation of Small Businesses said its members would be annoyed by the news as it appeared MPs were "treated differently" to other taxpayers.

If entrepreneurs sought professional tax advice, they had to pay the fee themselves and offset it against any profits, on which they paid tax, a spokesman said.

General taxpayers seeking advice on their self-assessment tax forms just had to pay the cost themselves, he added.

"What's happening with politicians, they have used tax advisers - and that's good as they say they want to get the tax right - but any fee they pay to accountants - they just get back on expenses.

"There's nothing illegal, it's in the Green Book [Commons rule book] , but then you get other taxpayers treated differently."

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